1. Field of the Invention
The present invention is related to optical networks and, in particular, to a coating for a micro-electromechanical systems (MEMS) mirror.
2. Background Information
Integrated circuits are formed on semiconductor wafer substrates by a number of processing steps. These steps include deposition, etching, implantation, doping, and other semiconductor processing steps well known to those skilled in the art. Thin films can be formed on wafer surfaces by a deposition process as well. These thin films can comprise, for example, silicon dioxide, doped glasses, silicides, etc. The thickness of such films usually ranges from about a few hundred angstroms to several micrometers. Often, three or more film layers are formed on the surface of a single semiconductor wafer. Deposition of such films can cause stress on the wafer, however.
In the art of fabricating semiconductor wafers, it is of known importance to minimize or control stresses in surface films. High surface stresses can cause the wafer to be deformed. For example, a compressive stress in a surface film will cause a wafer to slightly bow in a convex direction, while a tensile stress in a surface film will cause a wafer to slightly bow in a concave direction. Therefore, both compressive and tensile stresses cause the surface of the semiconductor wafer to deviate from exact planarity.
Lowering the temperature used when depositing a film can reduce stresses. Unfortunately, lowering the deposition temperature tends to lower the quality of the devices that will use the wafer. For example, when wafer processing is used in the manufacture of a micro-electromechanical system (MEMS) mirror, the stresses may tend to cause the mirror to bow slightly, and these deviations in the mirror's shape tend to cause coupling losses. MEMS mirrors tend to be very thin, on the order of a micron, and are particularly sensitive to stress. This is especially troublesome considering that current MEMS mirrors already tend to suffer from poor wavelength dependence, relatively low reflectivity, and other limitations, such as bandwidth and/or data rate limitations.